Sharks are renowned as apex predators in marine ecosystems and are often depicted in a sinister light with their wide jaws, sharp teeth and swift movements. Despite their formidable presence, they are not immune to threats, including being hunted and consumed as a source of fish protein. Annually, over 1.4 million tons of sharks, including 100 to 300 tons of bronze whaler sharks, are killed for consumption.
Over 200 countries around the world are involved in the legal and illegal import and export of shark products, including those in the shark fin soup trade. These products are used for various purposes including medicinal uses, fishmeal production for livestock feed and human consumption.
The high concentration of vitamin A in shark derivatives, shark liver oil being used as a lubricant in the tanning and textile industries, and the increasing popularity of shark fin soup have attracted a high demand for shark meat. Despite their economic demand, sharks have been found to possess exceedingly high levels of toxic contaminants. Even in supposedly unpolluted areas, they can contain high concentrations of trace elements and toxic contaminants compared to other aquatic organisms. This raises a critical question: how safe is shark meat for human consumption? Researchers from UCT have locked in to assess the levels of harmful chemicals in these fish, specifically bronze whaler sharks, and estimate the potential risk to consumers.
To answer these burning questions, a total of 41 bronze whaler shark (Carcharhinus brachyurus) carcasses were collected along the East and South coasts of South Africa off the Indian and the Southern Atlantic Oceans in 2022. Ten trace elements (Mercury, Arsenic, Chromium, Lead, Copper, Zinc, Aluminium, Cadmium, Magnesium, and Iron) known to be harmful to human health (and some, only toxic in excess amounts) were analysed in the muscular tissues of the species to assess potential health risks from consuming this shark species.

The study found that while all trace elements were within regulatory limits for human consumption, significant concerns arose regarding mercury and arsenic toxicity. An average adult meal serving (227 grams) of this shark meat contains 0.77 µg/kg of mercury, 8 times higher than the USEPA (United States Environmental Protection Agency) reference dose limit of 0.1 µg/kg of body weight. Since mercury in fish tissue primarily exists as methylmercury (MeHg), long-term exposure could lead to significant risks of mercury toxicity. Additionally, long-term consumers risk arsenic toxicity, as an average daily intake contains 0.5 µg/kg, which is twice the USEPA limit of 0.3 µg/kg for inorganic arsenic. Though below harmful limits, other trace elements may still pose long-term health risks.
Mercury and arsenic pose significant threats to human health, even in minute quantities, with compounding negative health impacts from continual bioaccumulation through long term consumption and exposure. It is essential to consider both the frequency and amount of shark meat consumed to mitigate these risks. Mercury toxicity can cause neurological damage, cognitive deficits, developmental issues in children, kidney damage, cardiovascular diseases, and immune dysfunction. Arsenic exposure increases the risk of cancers (skin, bladder, and lung), skin disorders, peripheral neuropathy, respiratory problems, and type 2 diabetes, along with reproductive and immune system effects.

Advice for consumers:
Given the potential health risks of consuming bronze whaler sharks, consumers should take several precautions to protect their health. These include:
- Low or moderate intake: If consumers must feed on bronze whaler shark meat due to socio-economic factors, they should reduce intake and limit the frequency and portion sizes in their diet. Occasional consumption may pose less risk than regular large servings. In terms of shark conservation, bronze whalers are listed as “Vulnerable” in the International Union for Conservation of Nature (IUCN) Red List, so harvesting and consuming them (especially in large quantities) might contribute to the extinction of this species.
- Diversifying seafood choices: Other aquatic animals at lower trophic levels are generally safer to consume due to their lower levels of contaminants. Fish such as salmon, tilapia, and tuna are generally safer options and provide similar nutritional benefits as shark meat without the high risk of toxic chemical exposure.
- Considering vulnerable populations: Special caution should be exercised for vulnerable groups, such as pregnant women, young children, and the elderly. These groups are more susceptible to toxic contaminants and should avoid high-risk seafood like bronze whaler sharks.
Policy implications:
To protect consumers, stricter regulations and improved monitoring of seafood for contaminants are necessary. Governments and regulatory bodies must implement rigorous testing protocols to ensure market seafood meets safety standards. This includes regular, comprehensive testing of seafood products for toxic elements and chemicals and promptly identifying and removing contaminated batches from the supply chain.
Additionally, about 50% of global shark landings come from bycatch – i.e. non-target species unintentionally caught in commercial fisheries. Therefore, implementing and enforcing regulations to reduce bycatch by using selective fishing gear (fishing gear that only catches the target fish) can significantly reduce the amount of potentially contaminated shark meat entering the food supply.
In conclusion, while shark meat, including that of bronze whaler sharks, is a significant protein source, it might carry potential health risks, particularly from Mercury and Arsenic and may cause cardiovascular diseases, neurological damage, cognitive deficits, and in severe cases, increased cancer risk. Given the IUCN classification of bronze whalers as “vulnerable”, reducing consumption would aid their conservation. To protect both human health and shark populations, the consumption of shark meat should be drastically reduced. The nutritional benefits offered by shark meat can be equally acquired from other fish such as tuna and salmon, which do not carry the same risk of toxic contaminants.
Written by: Adetola Adebowale Article: Bioaccumulated trace element toxicity in commercially harvested bronzewhaler sharks (Carcharhinus brachyurus) of South Africa. https://doi.org/10.1016/j.foodchem.2024.140081